The present invention relates to a skid control system in which the brakes are controlled by an integrating comparator which compares a current representative of wheel deceleration to a current which is altered to define a hypothetical wheel speed profile. More specifically, the reference current initially has a value representative of wheel deceleration occurring during an incipient skid condition. The integrating comparator receives the reference current and a current representative of wheel deceleration and provides an output signal when the current representative of wheel deceleration exceeds the reference current by a degree representing a predetermined decline in wheel velocity. The reference signal generator increases the reference current to a relatively high level in response to the output signal of the comparator. If the current representative of wheel deceleration exceeds this relatively high level within a predetermined period of time, the output signal from the comparator will be maintained thereby resulting in the release of the brakes. If the current representative of wheel deceleration does not exceed this relatively high level within the predetermined period of time, the output signal of the integrating comparator is terminated so that the brakes are not released. Presuming that the brakes are released, the reference signal generator reduces the reference current to a very low level at the expiration of the predetermined period of time. The output signal of the integrating comparator is terminated so as to initiate brake reapplication a predetermined period after the current representative of wheel deceleration no longer exceeds the reference current as determined by the integrating comparator. This period is established to approximate the time required for the wheel to spin up to the hypothetical wheel speed profile. On high mu surfaces, the current representative of wheel deceleration ordinarily will become sufficiently less than the reference current to terminate the output of the integrating comparator and reapply the brakes during the generation of the high level reference current. In the case of low mu surfaces, the current representative of wheel deceleration ordinarily will become sufficiently less than the reference current to terminate the output of the integrating comparator and reapply the brakes during the generation of the low level reference current.
The skid control system of the present invention utilizes a straightforward circuit of few components to provide skid control performance which meets or exceeds the performance of much more complex contemporary skid control systems. It may be readily constructed using conventional operational amplifiers. In view of the fact that operational amplifiers are mass produced in great quantities for a variety of uses and are therefore available at low cost, it will be appreciated that the skid control system of this invention can be produced at very low cost.